1. Field of the Invention
The invention relates to a multipart cooled piston for an internal combustion engine.
2. The Prior Art
A piston used in a diesel engine is known from European patent application 0 604 223 A1 and is comprised of an upper part and a lower part. The piston is assembled by screwing the upper part of the piston to the lower part of the piston via a threaded bolt inserted in the center of the upper part, and a threaded hole drilled into the bottom part. In order to obtain a permanent joint between these two parts of the piston, it is necessary to secure the screw connection with a lock nut. This has the disadvantage that when the piston is assembled, only a short piece of the threaded bolt appears between the hubs of the bolt, so that it is difficult to screw a lock nut to this short piece of the threaded bolt.
It is therefore an object of the invention to construct the upper and bottom parts of a multi-part piston in such a manner that the upper part can be mounted on the bottom part of the piston in a simple manner without the additional use of a lock nut or any other securing means.
This object is achieved according to the invention by a multipart cooled piston comprised of an upper part and a lower part of the piston, the upper part having a ring wall and a ring part which, jointly with the lower part of the piston, forms outer ring-shaped cooling channel and also an inner ring-shaped cooling channel arranged concentrically with the outer cooling channel. The lower part of the piston comprises a box-shaped piston shaft with two bolt hubs connected therewith, whereby the upper part of the piston, on the side facing the lower part of the piston, has a threaded bolt arranged coaxially with the longitudinal axis of the piston.
The lower part of the piston, on the side facing the upper part of the piston, has a threaded bore arranged coaxially with the longitudinal axis of the piston and comprises a female thread fitting the thread of the threaded bolt. The threaded bolt and the threaded bore are arranged so that the threaded bolt can be screwed into the threaded bore for assembling the upper part of the piston and the lower part of the piston. The threaded bolt forms an inner limitation of the inner cooling channel, and an area of the lower part of the piston that covers the inner cooling channel has the threaded bore and is thin-walled to such an extent that it can be deformed like a plate spring.
What is achieved in this manner is that when the upper part of the piston is screwed to the lower part of the piston, the thin-walled area of the bottom part of the piston that is provided with the threaded drilled bore, is vaulted upwards like a plate spring, so that after the piston has been assembled, a tensile stress is exerted on the threaded bolt. This results in a permanent joint between the upper and lower parts of the piston in the assembled condition.